In the Swedish patent 9103715-0, the corresponding International patent application PCT/SE92/00808 and U.S. Pat. No. 5,327,422 a multiplexer/demultiplexer is disclosed which is intended to be used in an STM-network ("Synchronous Transfer Mode") and which has memories of FIFO-type for smoothing or evening the input and output flow of data units in the multiplexer/demultiplexer. Such multiplexers/demultiplexers can use distributed configuration memories, which for a demultiplexer control the location to which the contents in different time slots are to be transmitted or for a multiplexer control the time slots to which different data stored in these FIFO-memories are to be forwarded. Several multiplexers/demultiplexers can be connected in a cascaded configuration and then problems can arise when changes of the configuration memories are to be made, e.g. involving that the data flow from a specific subscriber is to be increased or decreased. Messages concerning such changes are normally transmitted also in the same network and it cannot be guaranteed that such change messages arrive at the same time or at suitably chosen times to the different configuration memories. A configuration memory located closer to the destination of a considered data message from a subscriber can then obtain reconfiguration commands earlier than a configuration memory which is located earlier in the path along which the data message has to run when it is transfered from the subscriber to a central switch. Thereby data for other subscribers can be destroyed, these data flowing through the FIFO-memories associated with the configuration memories. Corresponding errors can occur, when the message passes out from the central switch through several cascaded multiplexer units.
The published British patent application GB-A 2 225 917 relates to a packet switched network and to updating of data after adding or removal of subscribers. The requirement for synchronism is avoided and a synchronism is produced. Changing subscriber data is made without influencing the communication of other subscribers.